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The procedure involves running a surgical-grade cord through the fistula tract so that the cord creates a loop that joins up outside the fistula. The cord provides a path which allows the fistula to drain continuously while it is healing, rather than allowing the exterior of the wound to close over. Keeping the fistula tract open can help keep from trapping pus or other infectious material in the wound. The procedure was mentioned by Hippocrates.
Setons can be tied tightly or loosely and with different materials, depending on the anatomical location of the fistulae and what may be medically required. A seton might be tied loosely as a palliative measure to avoid septic and painful exacerbations, or as temporary measure before surgical excision as in fistulotomy or fistulectomy. In some types of fistulae, a seton may be tied with more tension and tightened periodically. In this case, the seton loop will slowly cut through tissue inside the loop while scarring behind the loop, essentially "pulling out" the fistula without surgery. This is the Kshar-Sutra method mentioned by Sushruta in ancient Indian surgical practice.